74*245 Motor Driver

H-Bridge Driver

Simple PWM Gen.

Handy Method Measuring RPM

Measuring RPM via Photo reflector

Introduction to Robotic

DC, Stepper,and Servo Motor

Microcontroller Tutorial

Computer Interface
Tutorial
.............more links

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My First Line Follower (uC less)
by Rao

As most of the people here have been asking for the line follower schematic. I think this would be the most appropriate beginning towards the understanding of the line follower's working and applying this concept into a working robot. This is a microcontroller-less line follower as many of our members are yet not well versed with microcontrollers.

The basic building block of line following

The basic building block of a line follower consists of a comparator, an LED-Photodetector pair (IR or visible wavelength). As shown in the figure, the basic black line detecting circuit is made when the above mentioned components are connected in the following manner. The basic principle behind the working of a line follower is that black color absorbs light where as white reflects the light. This principle is exploited when we make a line follower.

The here we can see that the positive and negative ports of the line follower are connected to a 20k potentiometer and and the photodetector and a 10k resistor connected in the voltage divider connection respectively. Till there is no light on the photodetector, it has HUGE resistance and hence there is no voltage drop across this port and there is a comparitively higher voltage at the potentiometer tuned at half point. Now we make light fall exactly on top of the photodetector. What happens then is the electron band gap of the detector diode reduces and so does its resistance and it comes to something between 1k and 10k. at this time the voltage divider connection of the photodetector produces a voltage drop more than the potentiometer and hence the negative port becomes functional i.e. a positive pulse is emitted (in this case,

If you have connected an LED to the output of the comparator, then tune your potentiometer as the light falls on the photodetector and at a point (on the higher side i.e more than half) the LED will glow invariably. This means that this is the point where the voltage at positive port is more than that of the negative even when the photodetector is functional. Hence, the point just before this "invariable glow" point is the most sensitive point for the line follower. i.e distance of detection is maximum at this point.

Now all you have to do is to connect the output of the comparator into an L293D motor controller IC or your own H-Bridge and ground the other input (L293D or H-Bridge input) for a single direction wheel spin. For both directions, just connect an inverter to the comparator output and feed it to the other input. As most people are "somehow" facing problems with their L293D connections. Here is the schematic on how to go around with it.

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